Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, data, and so on. These systems may be multiple-access systems capable of supporting simultaneous communication of multiple wireless communication devices with one or more base stations.
Digital signal processing provides benefits to wireless communication systems and devices. However, the use of digital signal processing may require a digital to analog converter (DAC) to convert the digital signals to analog signals prior to transmission. Furthermore, the converted analog signals may need a frequency adjustment prior to transmission. The frequency adjustment may be accomplished using a local oscillator and a mixer. The local oscillator may generate a local oscillating frequency which is then mixed with the converted analog signals to obtain a transmit signal with the proper frequency.
The local oscillator may use digital components to generate the local oscillating frequency. The digital components may operate using a digital clock. The digital clock may cause interference signals (also referred to as spurs) to appear on the local oscillating frequency at frequency intervals of the digital clock. For example, a phase locked loop (PLL) may create spurs. Spurs may degrade the receiver band noise and cause the wireless communication device to fail out-of-band emission specifications.
Various spur reduction techniques exist. Some of the approaches include improving isolation through guard rings and deep n-wells, reducing power supply (Vdd) current magnetic coupling with local regulators and decoupling capacitors, changing spur frequency with programmable reference and filtering the spurs in the transmitter (Tx) or receiver (Rx) signal paths. For example, the spurs may be removed from the transmit signal using a surface acoustic wave (SAW) filter. Benefits may be realized by reducing or removing spurs without the use of a SAW filter.